Genetic studies to date have defined the properties of a dominant mutant allele (wDZL) at the white locus of Drosophila melanogaster. On the basis of the results of these studies I have concluded that this allele causes the repression of transcription of the white locus and that this allele exerts its effects in both the cis and trans configurations. We have recently cloned DNA sequences from the white locus region. In situ hybridization analysis to date demonstrates that the cloned sequences reside very near and probably within the region containing the white locus genetic elements.